This invention relates to a process for producing hydrophilic group-containing macromonomers having an ethylenically unsaturated group at the end thereof.
Hydrophilic group-containing macromonomers which are relatively low polymers having a radically polymerizable functional group and having a molecular weight of from about 1,000 to about 100,000 can be copolymerized with ethylenically unsaturated monomers to form graft copolymers. Such graft copolymers have excellent interfacial physical properties and therefore have been utilized as: coating; surface modifiers for resins; primers; adhesives; various binder resins; surfactants; dispersion-stabilizing agents; optical pattern-forming materials in combination with photosetting resins; anti-fogging agents; materials from which contact lenses are produced; and medical polymeric materials.
Prior processes for producing polymers having a radically polymerizable functional group at the end thereof are broadly classified into ionic polymerization processes and radical polymerization processes. Of the above, the ionic polymerization processes have a selectivity for a monomer and a solvent and therefore cannot be applied to the production of a hydrophilic group-containing macromonomer. On the other hand, the radical polymerization processes include a process of making addition polymer containing a terminal functional group reactible in a condensation reaction by polymerising ethylenically unsaturated monomer in the presence of an initiator and a chain transfer agent, each of which contains said functional group (see British Patent Specification No. 1,096,912).
By this process, a functional group which can undergo reaction in the condensation reaction can be introduced into the polymer end. In particular, when the molecular weight of the polymer is high, the process is particularly effective and can positively introduce the functional group. When the thus introduced functional group is reacted with an epoxy compound having a vinyl group, the vinyl group can be introduced into the polymer end.
However, no hydrophilic group-containing macromonomer having an ethylenically unsaturated group at the end thereof and no process for producing the same have been heretofore known. This is because it is thought that the following reaction occurs: even if a relatively low molecular weight hydrophilic group-containing polymer containing hydrophilic groups such as hydroxyl and methylol groups in the polymer and having a functional group such as a carboxyl group at the polymer end is obtained, it is difficult to selectively vinylate the terminal carboxyl group with a vinyl group-containing epoxy compound because a competitive reaction with hydroxyl and methylol groups simultaneously occurs.
Further, in order to lower the molecular weight of the terminal functional group-containing hydrophilic polymer which is a starting material of the process of the present invention, it is necessary to add a large amount of a chain transfer agent to the polymerization reaction system. The chain transfer agent remains after polymerization. If the reaction mixture is used as the starting material as it is, a graft copolymer having a high molecular weight cannot be obtained. If the remaining chain transfer agent is to be removed, an extra purification step will be required.